DE20023848U1 - Device for applying atomized fluids, e.g. for rapid prototyping, has ultrasonic atomizers supplied with fluid essentially arranged above defined region to which atomized fluid is to be applied, at least one is movable over defined region - Google Patents

Abstract

The device for applying atomized fluids has at least two ultrasonic atomizers (1A) that are supplied with the fluid essentially arranged above the defined region to which the atomized fluid is to be applied. At least one of the ultrasonic atomizers can be moved over the defined region.

Description

The The present invention relates to a device for applying of atomized Fluids. Furthermore, the invention also relates to the use of a such device.

In Many areas of technology require fluids and that especially liquids atomized into very fine particles can and can thereby in one possible exact quantity and in a fine distribution atomised and thereby, for example, can be applied to another layer.

In certain rapid prototyping processes, for example, a coating of binder plays an important role. From the DE 198 53 834.0 is such a rapid prototyping method for building cast models known. Here, an untreated particulate material, such as quartz sand, is applied to a building platform in a thin layer. Thereafter, with the aid of a spray device, a binder is sprayed onto the particulate material in as fine a distribution as possible, and thereafter a hardener is metered onto selected areas, whereby the desired areas are solidified. If this process is repeated again and again, an individually shaped body of the bound particulate material can be provided. This body is initially embedded in the surrounding, unbound particulate material and can be removed from the particle bed after completion of the construction process.

Becomes For example, in such a method as a particulate material a quartz sand used and as a binder, a furan resin with the help of a sulphurous acid as hardener material one Molds are made that are commonly used in model making used and therefore known in the art materials.

difficulties in these known methods are usually justified in the entry of the binder. Around To be able to produce a suitable mold, this mold must be determined Requirements for strength and binder content are sufficient.

To the One must the Strength sufficient to withstand the pressure of the liquid metal during casting to be able to or the buoyancy forces in the case of the formation of a core without disturbing deformation in the core bearing to derive.

To the Others must the Binder content, however, if possible be low, so when pouring the Metal vaporizing binders fail to gas inclusions and thus to a lesser quality of the casting leads. One possible low binder content favors In addition, the demolding of the casting, as the casting evaporates much of the binder. When using as little as possible Binder remains after casting of the component essentially only loose, easy to remove Sand back.

The Application method of the binder is therefore particularly important since in this case the binder content and the binder distribution of Casting models are set. It often causes difficulties that it is the binder to a highly viscous liquid which is difficult to finely distribute.

The Requirements for a device for applying, for example, one Binders on a layer of particles are the binder in a homogeneous and predetermined distribution on the surfaces of the Apply particles without them in their shape and their Influence distribution.

Out The prior art has various possibilities for atomization of Fluids known.

So become common Hochdruckzerstäuber used to liquids with similar ones Fluid properties, such as that of the binder, very finely distributed. Hochdruckzerstäuber to press the fluid to be distributed usually with more than 20 bar through a narrow nozzle. This forms a liquid lamella, which disintegrates into individual drops. The drops are on such a sputtering on a solid surface according to the lamellar shape annular around a center with lower Drop density and a concentric area with high drop density distributed.

There however, the kinetic energy of those formed with a high pressure atomizer Drops are relatively high, may be a loose powder bed, on the binder should be applied, only by a large distance from the nozzle protected against blowing become. As a result, however, an undesirably high space requirement is involved such an atomizer necessary and continue to be subject to the drops on the long way from the formation of drops to the place of application also external influences.

Another problem with these high pressure atomizers is the large dead time in the start and stop operations. Until after pressure has been applied to the nozzle, a lamella and thus also the droplet separation has formed, there arises a larger fluid drop, which separates abruptly and the uniform distribution of the fluid significantly disturbs. This also applies when the pressure is switched off. In addition, this effect is aggravated by compliances or inaccuracies in the system, which lead to a further dripping of binder.

Another atomizing device is in the EP 0 049 636 A1 disclosed. This device also works with form in a nozzle chamber. However, the droplet decay is generated by an electric vibrator, which is controlled for example via a piezoelectric actuator.

at all of these, with nozzles working atomizers It has proved to be disadvantageous that the very small nozzle diameter tend to clog. This is especially true during use from toughening liquids heavy in weight. Larger nozzle diameter on the other hand tend to an air sucking into the nozzle chamber and thus to a strong loss of effect.

In WO 98/00237 a droplet cloud generator is presented, which, with fluidically effectively arranged piezoelectric transducers within a fluid-filled chamber, pressurizes an entire array of nozzles, which is caused by droplet ejection. In contrast to that from the EP 0 049 636 A1 known principle, however, no form is necessary.

But Also this system tends to clog due to the small nozzle diameter. Furthermore is the life of such a droplet cloud generator, in particular when using high viscosity liquids, such as Binders, relatively short.

Farther it is also known from practice to use air atomizers. This breaks a shell air flow finest droplets from a capillary. This type of atomization is especially in the Painting technique used. For example, in an application for binders, which is to be applied to loose particulate material, blown the Mantelluftstrom undesirably also the particle material. About that In addition, difficulties or irregularities arise here as well when switching the atomizer on and off.

Also Is it possible, that fine droplets, for example, over a rotary atomizers be applied to a predetermined area. It is about a Rotation a thin one liquid lamella produced, which disintegrates into individual drops. However, it is also at one such device the startup behavior for an application in which the Fluid is to be applied very accurately, very detrimental.

From the US 4,796,807 An ultrasonic atomizer for atomizing low-viscosity fluids is known. These ultrasonic atomizers consist of an actuator element, usually a piezoceramic, a liquid supply and depending on the purpose of an air duct. The piezo actuator oscillates during its operation at a high frequency. The fluid is located on a vibrating plate and is thrown off by the surface effects generated by the vibration in the liquid. An air stream leading around the actuator picks up the droplets, which are provided with a relatively weak impulse, and conveys them further in an air flow.

Such ultrasonic nebulizer These days air conditioning is used to control the humidity in the air Admixture of water droplets to discontinue or even in medical technology to drugs like that prepare them to be inhaled by a patient.

at has such known from the prior art ultrasonic atomizer it proved to be disadvantageous that in an order of fluids In a limited field, a relatively large amount of time is required to do so a uniform homogeneous To achieve distribution of the fluid.

It It is therefore an object of the present invention to provide a device with a relatively short time a homogeneous distribution from to be atomized Fluid can be achieved and in which the problem of clogging of nozzles can be prevented.

According to the invention this Task solved with a device for applying atomized fluids by means of ultrasonic atomizer a predetermined range, wherein at least two ultrasonic atomizers, the be supplied with the fluid, substantially above the predetermined Area, as seen in the direction of the plot, are arranged.

Thereby, that now at least two ultrasonic atomizers substantially above are arranged at the predetermined range, can at least over a sputtering through the two atomizers formed area a relatively homogeneous spray pattern of the atomized fluid be achieved. In this case, the distance between the at least two ultrasonic atomizers should be different preferably chosen such be that from the atomizer emerging spray material overlaps in a certain range.

If the predetermined area is an area that extends at least in the width and / or in the depth, than that of reached the ultrasonic atomizers, the device is provided in an advantageous embodiment such that at least one of the ultrasonic atomizer over the predetermined range is movable. Thus, it is also possible to apply fluid to a larger area by means of ultrasound atomizers.

The Traversing the ultrasonic atomizer can in addition to the extension directions of the given area also a height mobility umfasssen. Are the ultrasonic atomizers also movable in height, so the distance to the given area, depending on the application, Fluid, ambient conditions, etc. are set.

are the at least two ultrasonic atomizers side by side, one behind the other and / or staggered to each other, so even better homogeneous Distribution of the sprayed material be achieved. In a corresponding arrangement of the ultrasonic atomizer can the application in their distribution of the spray material on the area, such as desired set become.

Furthermore can, depending on the size of the the atomized Fluid area also at least four or even more more ultrasonic atomizers be provided.

is at least one or even all ultrasonic atomizers with an air duct provided, so to be atomized Particles even better distributed on the given area. Without an air supply the atomized ones move Particles exclusively due to its gravity from the ultrasonic atomizer to the given area, such as a working surface. The application image of the atomizer corresponds without air supply in the cross section of the exit surface the atomizer. To a wider area Order to reach, The particles are preferably fanned out by a conical air guide.

To the Reaching an air duct can the supplied Air can be put into a strong rotation by baffles and as a rotating, cylindrical air mass next to the vibrating one Surface of the atomizer escape. The atomized Fluid is entrained by this airflow and by the circulation The air expands conically after exiting the atomizer.

These Air circulation, for example, by inserted into the ultrasonic atomizer, be achieved with baffles provided with baffles, wherein the Deflector plates individually adjusted according to their twist direction and spin strength can be.

Commercially used atomizer generally have a uniform spin direction of the air duct. This however, it can be detrimental the so-called spray picture, So the application area of the Zerstäubergutes lead, because in the overlap area the atomized Particles collide at opposite speeds. To a resulting mutual disturbance of the flow of the atomized particles curb, should the Luftrotationsrichtungen adjacent ultrasonic atomizer with air duct advantageously opposite to each other.

Around several, according to the invention used with ultrasonic atomizers To supply a fluid, it is important that the fluid to all Atomizer on an equal footing is distributed. About that In addition, the supply of the fluid should be independent of the number of connected Be an ultrasonic atomizer, to turn on or off of atomizers during the life of the device to enable. Furthermore, such a device should promote the most accurate flow.

To This purpose is now a central feed of the invention Fluids selected, for all ultrasonic nebulizer provides a constant pressure of the fluid. The feeder is designed in this way that the housing and cable cross-sections are designed so that in the existing flow rates does not set pressure drop in the system.

Become according to a preferred embodiment high viscosity fluids such as binders is used the influence of temperature on the viscosity and with a pressure conveyor too on the flow rate considerably.

Around to take account of this fact and to counteract such external influences the necessary pressure, which leads to the desired flow rate, depending on Temperature and fluid used via a suitable pressure control system set variably. The pressure is constantly during the term of the application the external conditions customized.

Around the ultrasonic atomizers each have to provide the same amount of medium, the feeding be calibrated before use. All systems must be Medium the same flow resistance Offer. This will be done according to a preferred embodiment achieved by the use of chokes, each with a Ultraschallzerstäuber a Throttle is connected upstream.

According to a particularly preferred Aus Guidance form, the control of the ultrasonic atomizer is designed such that it is an adaptive control. Such controls are usually very difficult, since an adaptive frequency control is necessary due to the higher density of a binder preferably used, because for atomization of highly viscous fluids, the highest possible amplitude is necessary.

This As a result, the piezoceramic used as the actuator always stimulated with the natural frequency of the whole system piezoceramic plus attachments must be to a maximum vibration amplitude on the vibrating plate to achieve and thus optimally atomize the highly viscous liquid. in this connection it is now problematic that the natural frequency during the Operation changes. Around always achieving a maximum oscillation amplitude is an adaptive one Regulation required.

Further give advantageous embodiments of the present invention from the dependent claims and the description. For a more detailed explanation the invention will be based on preferred embodiments below described in more detail with reference to the drawing.

In the drawing shows:

1 an ultrasonic atomizer in a schematic, partially sectioned view according to a preferred embodiment;

2 a schematic representation of the effect of an air duct in an ultrasonic atomizer according to another preferred embodiment of the invention;

3 a swirl plate for generating an air duct;

4 an exemplary arrangement of two ultrasonic atomizers, and their respective and their total drop distribution;

5 an arrangement of the ultrasonic atomizer in a view from above, according to yet another embodiment of the invention;

6 the spin direction of two juxtaposed ultrasonic atomizers in a view from above;

7 a schematic representation of a supply of the fluid to the ultrasonic atomizers according to a preferred embodiment; and

8th a circuit diagram of a control.

exemplary will be in the following the device according to the invention for use for atomising Binders as a fluid, for example for the layered construction of Cast models of particulate material, binder and hardener are explained.

at Such a construction method of a component, such as a cast model, becomes a build platform on which the mold is to be built a layer thickness lowered. Thereafter, particulate material, such as quartz sand, in a desired layer thickness applied to the build platform. This is followed by the application of the binder, essentially over a large area the particulate material, which then selectively on the cured Areas hardener is applied. This can be achieved, for example, by means of a drop-on-demand drop generator, in the manner of an inkjet printer. These application steps be repeated until the finished part, embedded in loose Particle material is obtained.

In the 1 is now an example of the structure of a Ultraschallzerstäubers 1A for applying binder shown. The principle of an ultrasonic atomizer used according to the invention 1A is preferably based on a power ultrasound transducer with an amplitude transformer.

In such a power ultrasound transducer, the amplitude of the longitudinal vibration of a piezoceramic, which is actually insufficient for the atomization of liquids, is amplified by an amplitude transformer on the radiating surface of a transducer. In the embodiment shown here is a so-called step horn 3 used by the piezo actuators 2A . 2 B introduced vibration energy concentrated on a small area, the so-called radiating surface, and thus greatly increases the amplitude of this vibration.

The two piezoactuators 2A . 2 B be doing this by means of a clamping nut 4 on a step horn 3 clamped and with the help of a contact foil 5 and a fastening film 6 contacted. Due to the opposite arrangement of the piezo actuators 2A . 2 B If there is an activation, an increase in thickness takes place in both directions.

In addition, a shim may be the piezo actuators 2A . 2 B to protect the entire system against a large temperature dependence from damage during assembly and by a different thermal expansion coefficient compared to steel.

According to the illustrated embodiment of the invention, the ultrasonic atomizer 1A formed with an air guide. In the 2 Now the effect of the air duct is shown in more detail. It shows the 2A an ultrasonic atomizer 1A without air supply and the 2 B with supplied air 7 , Again 2A can be seen, move the atomized liquid particles 8th usually only by their own gravity from the ultrasonic atomizer 1A to the working surface to which they are to be applied. There is therefore an atomization image which is in the cross section of the exit surface of the ultrasonic atomizer 1A similar. To achieve a larger area application, the atomized fluid 8th , here binder, preferably by supplied air 7 , which results in a conical air guide, fanned out.

The supplied air 7 is doing by baffles 9 placed in a strong rotation and occurs next to the vibrating surface of the ultrasonic atomizer 1A as a rotating, cylindrical air-fluid particle mass. The atomized binder 8th is entrained by the air flow and widened conically by this circulation of air. This is in the 2 B shown schematically by the arrows.

The resulting cone angle of the exiting air-binder particle mass is dependent on the geometry of the baffles 9 , the exit cross section of the ultrasonic atomizer 1A and the pressure of the supplied air 7 ,

As already mentioned, the air circulation through inserted swirl plates 10 that with baffles 9 are provided, and which can be adjusted individually according to twisting and twisting strength achieved.

In the 3 is an example of such a swirl plate 10 with thereon arranged baffles 9 shown.

A device according to the invention is characterized in that at least two ultrasonic atomizers 1A . 1B substantially above the predetermined area to which the atomized fluid is applied.

Now become ultrasonic atomizers 1A . 1B used with spray cones generated by air ducts, by juxtaposing the ultrasonic generator and thus also the spray cone, a homogeneous spray pattern of the atomized binder 8th be achieved. This is schematically in the 4 shown. Here is the droplet distribution, so the zer dusted binder 8th on a region to be coated, of an ultrasonic atomizer 1A thinner dashed and the other ultrasonic atomizer 1B shown in bold dashed lines.

The overall distribution of the atomized binder shown as a solid line 8th on an area is like that 4 can be seen, essentially a flat distribution, as it is usually desired. The distance of the individual ultrasonic atomizers 1A . 1B each other depends on the distance of the ultrasonic atomizer 1A . 1B from that with the atomized binder 8th To be provided area, as here, for example, a surface to be coated.

A typical distance of the ultrasonic generators 1A . 1B to the surface to be coated is 140 to 160 mm. This has a lateral distance of the ultrasonic atomizer 1A . 1B each other of about 45 mm proved to be advantageous.

In the 5 is now an advantageous arrangement of the ultrasonic atomizer 1A . 1B . 1C . 1D shown in a view from above. There are four ultrasonic atomizers exemplarily 1A . 1B . 1C . 1D arranged, however, could continue to the left and to the right respectively in this in the 5 shown manner further ultrasonic generators are arranged.

In this inventive arrangement of the ultrasonic atomizer 1A . 1B . 1C . 1D The systems are laterally offset from each other on a support 11 arranged. In this way, the required distances of the ultrasonic atomizers 1A . 1B . 1C . 1D be well respected. Furthermore, by the method of the carrier 11 also a uniform procedure of all ultrasound atomizers 1A . 1B . 1C . 1D be achieved if desired.

The direction of rotation or air rotation direction achieved by the air guide described in more detail above 12A . 12B the ultrasonic atomizer 1A . 1B . 1C . 1D is in commercial ultrasonic atomizers 1A . 1B . 1C . 1D mostly uniform. This means that in a juxtaposition of the ultrasonic atomizer 1A . 1B . 1C . 1D The sputtering can be affected, as in the overlap point of the supplied air 7 generated cones of atomized binder 8th these collide at an opposite speed.

To avoid this, is in the 6 an advantageous embodiment juxtaposed ultrasonic atomizer 1A . 1B represented, wherein the Luftrotationsrichtung by the arrows 12A . 12B is shown. It will now according to the preferred embodiment shown the collision of the atomized fluid or binder 8th counteracted at an opposite rate such that adjacent ultrasonic atomizers 1A . 1B an opposite direction of air rotation 12A . 12B exhibit. In such an embodiment, the disturbance of the flow of the fluid in the overlapping region of the "Fluid cone" significantly reduced.

According to the invention, at least two or more ultrasonic atomizers 1A . 1B . 1C . 1D . 1E used. To these ultrasonic atomizers 1A . 1B . 1C . 1D . 1E all with the fluid to be atomized 8th to supply the binder is in the 7 a device according to the invention shown, in which all ultrasonic atomizers 1A . 1B . 1C . 1D . 1E Equally supplied with the fluid.

In addition, in such a feeder, the number of connected ultrasonic atomizer 1A . 1B . 1C . 1D . 1E , variable. Also is an on or off the ultrasonic atomizers 1A . 1B . 1C . 1D . 1E without allowing other impairments. Furthermore, a precise maintenance of the flow rate of the fluid is possible.

A central feeder is now selected for. all ultrasonic atomizers 1A . 1B . 1C . 1D . 1E provides a constant pressure of the medium. Basically, the housing and cable cross-sections are chosen such that sets no pressure drop in the system at the existing flow rates.

In this case, according to the preferred embodiment shown, since highly viscous fluids, namely preferably binders, are used, the influence of temperature on the viscosity and thus also on the flow rate in a pressure conveyor is considerable. To take this fact into account, the necessary pressure, which leads to a desired flow rate, depending on the temperature and the fluid used via a suitable pressure control valve 13 set variably. The pressure is thus constantly adapted at runtime of the device to the external conditions.

To finally the ultrasonic atomizers 1A . 1B . 1C . 1D . 1E each supplying the same amount of fluid, they must be calibrated before use. All ultrasonic atomizers 1A . 1B . 1C . 1D . 1E must provide the fluid with the same flow resistance. This is according to the shown before ferred embodiment through the use of throttles 17A . 17B . 17C . 17D . 17E achieved, the respective ultrasonic atomizers 1A . 1B . 1C . 1D . 1E upstream.

The fluid is in a pressure vessel 14 filled and by means of the pressure control system 13 brought to the necessary pressure. The fluid flows from there into a distributor 15 and becomes via lines to the chokes 17A . 17B . 17C . 17D . 17E led, in turn, the ultrasonic atomizer 1A . 1B . 1C . 1D . 1E supply with the fluid. Via additionally interposed valves 16A . 16B . 16C . 16D . 16E can the respective ultrasonic atomizers 1A . 1B . 1C . 1D . 1E each switched on or off. Controlled in this way, it is not always necessary to coat the same entire surface with the binder, but only as much as necessary. As a result, a saving of the binder is possible.

In the 8th is now an example of a logic diagram of a preferably used control for the ultrasonic atomizer 1A . 1B . 1C . 1D . 1E shown. The task of a control is generally the ultrasonic atomizers 1A . 1B . 1C . 1D . 1E with their natural frequency to achieve a maximum vibration amplitude on the vibrating plate. The problem, however, is that usually the natural frequency changes during operation and thus an adaptive control of the frequency must be made.

An ultrasound generator 1A has in its resonance range a defined course of its electrical impedance I. This course is in a digital controller 20 , such as a microcontroller, deposited such that first a conversion of the impedance I in the voltage U by means of a device 18 he follows. Thereafter, this analog signal is in an analog / digital converter 19 converted into a digital signal and the regulator 20 fed.

The controller controls a controllable oscillator 22 , whose output voltage to the necessary conditions with the help of an amplifier 23 amplified and via a transformer 24 is transformed. The ultrasonic atomizer 1A This signal is supplied and thereby causes an oscillation desselbigen.

If now the oscillator frequency is varied slightly and at the same time the impedance of the ultrasonic atomizer 1A measured, the controller detects 20 , whether the natural frequency of the ultrasonic atomizer 1A is reached. If this is not the case, it can be decided whether the frequency of the oscillator must be increased or decreased by the current natural frequency of the ultrasonic atomizer 1A to reach.

Because the regulator 20 the course of the electrical impedance and the possible range of the natural frequency of the ultrasonic atomizer 1A In addition, it can be easily ascertained whether an oscillation takes place in resonance or not and thus the function is checked and oscillations in undesired modes are prevented.

Such a regulation is permanent, which in the 8th represented by the closed circuit.

With a device according to the invention For spraying fluids, it has proven to be particularly advantageous that no nozzle sections susceptible to clogging are necessary, since ultrasonic atomizers 1A . 1B . 1C . 1D . 1E be used. Furthermore, the ultrasonic atomizers have no star ke air flow, which can sand a sand on which, for example, binder is to be applied. In addition, it has proved to be advantageous that the drop ejection is very uniform and thus is unproblematic by the on and off or on and off.

Farther These ultrasonic atomizers have one very long life, produce small drop diameter and have a low power consumption. In particular, with a control, such as As described above, an ultrasonic atomizer is particularly easy to control.

1A to E

ultrasonic nebulizer

2A, 2 B

piezo actuators

3

step horn

4

locknut

5

Contact sheet

6

attaching sheet

7

air supply

8th

Atomized fluid

9

baffles

10

airguides

11

carrier

12A, 12B

Air rotation direction

13

Pressure control system

14

pressure vessel

15

distributor

16A to E

valves

17A to E

throttle

18

Impedance-voltage converter

19

Analog to digital converter

20

digital regulator

21

Digital to analog converter

22

Voltage-to-frequency converter

23

amplifier

24

transformer

Claims (14)

Device for applying atomized fluids by means of an ultrasonic atomizer to a predetermined area, wherein at least two ultrasonic atomizers ( 1A . 1B . 1C . 1D . 1E ), which are supplied with the fluid, substantially above the predetermined range, as seen in the direction of application, are arranged. Device according to claim 1, wherein at least one of the ultrasonic atomisers ( 1A . 1B . 1C . 1D . 1E ) is movable over the predetermined range. Apparatus according to claim 1 or 2, wherein the at least two ultrasonic atomizers ( 1A . 1B . 1C . 1D . 1E ) are arranged side by side, one behind the other and / or offset from each other. Device according to one of the preceding claims, wherein at least four ultrasonic atomizers ( 1A . 1B . 1C . 1D . 1E ) are provided. Device according to one of the preceding claims, wherein at least one ultrasonic atomizer ( 1A . 1B . 1C . 1D . 1E ) is provided with an air duct. Apparatus according to claim 4, wherein the atomized particles ( 8th ) through the air guide on exiting the ultrasonic atomizer ( 1A . 1B . 1C . 1D . 1E ) are widened conically. Apparatus according to claim 5 or 6, wherein the air duct through by a swirl plate ( 10 ) passed through air is formed. Device according to one of claims 5 to 7, wherein at least two ultrasonic atomizers ( 1A . 1B . 1C . 1D . 1E ) Have air ducts which have opposite directions of air rotation ( 12A . 12B ) exhibit. Device according to one of the preceding claims, wherein the fluid is a highly viscous liquid, in particular a binder for Molding sand, is. Device according to one of the preceding claims, wherein a pressure with which the at least two ultrasonic atomizers ( 1A . 1B . 1C . 1D . 1E ) are supplied centrally with the fluid, is constant. Apparatus according to claim 10, wherein the pressure is due to external factors is adjusted. Device according to one of the preceding claims, wherein in front of the ultrasonic atomizers ( 1A . 1B . 1C . 1D . 1E ) one throttle each ( 17A . 17B . 17C . 17D . 17E ) is provided for a supply of the fluid. Device according to one of the preceding claims, wherein the ultrasonic atomizers ( 1A . 1B . 1C . 1D . 1E ) are individually switched on and off. Device according to one of the preceding claims, wherein a control of the ultrasonic atomizers ( 1A . 1B . 1C . 1D . 1E ) is adaptive.